Places · Dark sky
Bannau Brycheiniog Dark Sky Reserve
The first reserve in Wales, an hour from three million people, which is the point: it demonstrates that dark skies survive next to cities when lighting is controlled rather than removed.
- Where
- Wales, United Kingdom
- Coordinates
- 51.88°N 3.44°W
- Since
- 2013
- On the map
- Show me
- More
- darksky.org
The sky from here
The sky over this spot is zone 4 — suburban edge, Bortle 4–5, with a naked-eye limit around magnitude 5.7–6.5. The Milky Way is a faint band overhead and gone lower down. The sky is noticeably grey rather than black.
Against that sky 99 of the 110 Messier objects are straightforward in 10×50 binoculars and 100 in a 130mm, with 21 reachable by eye alone. The nearest sky of Bortle 2 or better lies about 44 km north-west of here.
Between 21 May and 22 July the Sun never gets eighteen degrees below the horizon from this latitude, so there is no astronomical darkness at all for those 63 nights. Nothing faint is observable in that window, however far you drive from the nearest town.
The galactic centre tops out at 9° from this latitude — low enough that the busiest part of the Milky Way is always behind the most atmosphere, which is what separates this sky from a southern one. Of the 110 Messier objects, 22 never set from here and every one of them rises at some point in the year.
The sky here is kindest to Spindle Galaxy, Whirlpool Galaxy and Sunflower Galaxy, each of which passes within a few degrees of overhead — an object at the zenith is being seen through the least air it will ever be seen through, and the difference against the same object low in the south is not subtle.
Little Dumbbell, Pinwheel Galaxy and Owl Nebula never set from this latitude, so they are available on any clear night of the year rather than for one season of it.
Read at 51.88°N 3.44°W. Darkness is estimated rather than measured; everything else follows from the latitude and holds along the whole parallel. How accurate this is.
Nearby
Questions
What part of the sky never rises at Bannau Brycheiniog Dark Sky Reserve?
Everything south of declination −38°. From 51.9°N that is a cap 52° in radius centred on the south celestial pole, which is 19% of the whole celestial sphere. That part of the sky is not merely a winter object or a difficult one; it is geometrically unavailable from this latitude. The equivalent cap around the north celestial pole is the compensation, and it never sets.
How many hours of true darkness does Bannau Brycheiniog Dark Sky Reserve get?
Anything from 12 hours 3 minutes down to none whatsoever. Around 21 December the night is as long as it gets here, and around 21 May the sky simply never finishes darkening — a problem no amount of driving solves, because it is the Sun's depression angle and not the streetlights. Astronomical darkness is the Sun more than eighteen degrees below the horizon, which is a stricter thing than the Sun being down.
When is the Milky Way best from Bannau Brycheiniog Dark Sky Reserve?
August and early September, which is a compromise rather than an optimum. The core transits at local midnight around 17 June wherever you are, but 51.9°N spends that part of the summer without any astronomical darkness at all, so the peak is unusable. The workable window opens when the nights return and closes as the core sinks into the evening twilight — a few weeks, and the reason northern observers travel.
How far is Bannau Brycheiniog Dark Sky Reserve from the other sites on this map?
Its closest neighbour on this map is Exmoor National Park, 85 km away to the south. That is also the nearest other dark sky, with the next one 1,030 km beyond it. Distances are great-circle, so they are what a signal covers rather than what a road does.